According to whether the base material is melted and the pressure applied, people divide the welding methods into three categories: fusion welding, pressure welding and brazing.
① Fusion welding Use a certain heat source to heat the weldment joint to a molten state (no pressure is applied), and then cool and crystallize to form a weld. When the welded metal is heated to a molten state to form a liquid molten pool, the atoms are fully diffused and closely contacted, and a firm welded joint is formed after cooling and solidification. Commonly used fusion welding methods mainly include electrode arc welding, submerged arc welding, electroslag welding, gas shielded welding, plasma arc welding and so on.
② Pressure welding must be applied to the weldment (heating or not heating) during the pressure welding process. One is to heat the welded metal contact part to a plastic state or a partial melting state, and then apply a certain pressure to make the metal atoms combine with each other. Firm welded joints, such as forge welding, resistance welding, diffusion welding, friction welding, etc.; the second is no heating, and only enough pressure is applied on the contact surface of the welded metal to cause plastic deformation, so that the original inter-phase does not rub against Until a firm joint is obtained, such as cold pressure welding, explosive welding, etc."
③ Brazing uses a material with a lower melting point than the base material as the brazing filler metal, heats the weldment and the brazing filler metal to a temperature higher than the melting point of the brazing filler metal but lower than the melting point of the base metal, and uses capillary action to fill the joint gap with the liquid brazing filler metal to melt the brazing The material wets the surface of the base material, and after cooling, the resultant product forms a metallurgical bond at the joint. The brazing method is divided into soft brazing and brazing. Depending on the heating method, flame, electric furnace, resistance, salt bath, ultrasonic and other heating can be used respectively.
Arc is a widely used welding heat source, mainly used for fusion welding. Electric welding or resistance welding uses resistance heat for welding. Friction welding, cold pressure welding and diffusion welding use the thermal energy of mechanical energy cable to weld, through top pressure, hammering, friction and other means. Plastic rheology occurs in the joint of the workpiece, destroys the metal oxide film on the joint surface, and acts on the external force. The oxide is extruded to realize the metal-to-metal connection. Gas welding relies on the mixed combustion of combustible gas (such as acetylene, natural gas, liquefied petroleum gas, etc.) and oxygen to produce the heat required for welding, surfacing or cutting.
